ABB REL670 2.2 IEC - Page 277

equivalent zero sequence circuit of the parallel lines will be according to figure
139.
Z Z
0 m0
Z Z
0 m0
Z
m0
A
B
C
99000039.vsd
I
0
I
0
DOCUMENT11520-IMG7100 V1 EN-US
Figure 140: Equivalent zero-sequence impedance circuit for the double-circuit
line that operates with one circuit disconnected and earthed at both
ends.
Here the equivalent zero sequence impedance is equal to Z0-Z0m in parallel with
(Z0-Z0m)/Z0-Z0m+Z0m which is equal to equation 193.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN-US (Equation 193)
The influence on the distance measurement will be a considerable overreach, which
must be considered when calculating the settings. It is a recommendation to use a
separate setting group for this operation condition since it will reduce the reach
considerable when the line is in operation. All expressions below are proposed for
practical use. They assume the value of zero sequence, mutual resistance R0m
equals to zero. They consider only the zero-sequence, mutual reactance X0m.
Calculate the equivalent X0E and R0E zero-sequence parameters according to
equation
194 and equation 195 for each particular line section and use them for
calculating the reach for the underreaching zone.
R R
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ +
+








DOCUMENT11520-IMG3502 V2 EN-US (Equation 194)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ −
+








DOCUMENT11520-IMG3503 V2 EN-US (Equation 195)
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 271
Application manual